Power transformers, reactors, condensive bushings as well as other high voltage equipment are largely used in electric power generation, transmission and distribution systems, where they perform several essential roles, such a way that the continuity of the power supplying depend, for the most part, upon the reliability of such equipment.
The aforementioned high voltage equipment frequently use, as an insulating and heat removing mean, some type of either oil or insulating liquid, that may be mineral oil (petrol derived), vegetable oil (obtained from soy bean, from sunflower or from other source) or silicon, among others, henceforth simply referred either as “insulating oil” or “oil”. All active parts of the equipment—core, windings, insulations, etc.—are immersed in insulating oil, in order to impregnate the paper and to assure the electric insulation of the assembly, besides providing the cooling of the active parts by means of such oil circulation in heat radiators.
Therefore, any inside fault occasionally occurred in an equipment, such as overheating points, bad contacts, partial discharges, arcs and others may provoke either oil or paper molecule breakage, generating gases that will dissolve into the oil. Types and volume of generated gases depend upon the kind of fault, upon its severity, upon the energy it may liberate as well as upon the materials involved in such fault (oil, paper, cupper, etc.).
Therefore, the measurement of those gases dissolved into the equipment may be used as a tool for a diagnosis of such equipment's status, allowing estimating existence (or not) of occasional defects, their nature and their intensity. With such measurements in hands, several techniques may be used for such data analyzing as well as for obtaining a diagnosis on the equipment status—transformer, reactor, etc. For clarification purposes, methodologies of the international standard IEC 60599—Mineral oil-impregnated electrical equipment in service—Guide to the interpretation of dissolved and free gases analysis as well as the Duval technique may be mentioned among others.
Such measurement has been traditionally made, at least since the 60's decade, by means of a laboratorial analysis of an oil sample taken from the equipment, from which the dissolved gases are extracted and gas-chromatographically analyzed. More recently, starting from the 80's decade, the first on-line gas monitors appeared, which are permanently installed at the high voltage equipment where they continuously measure dissolved gases in real time.
Due to the importance of high voltage equipment for the reliability of the electric power generation, transmission and distribution, the on-line monitoring of gases dissolved in insulating oil has become an each time more common practice for the diagnosis as well as the prognosis in real time of the status of the equipment, for it allows detecting and diagnosing occasional faults with greater efficiency and quickness than samples laboratorial analysis, avoiding therefore interruptions in power supplying, or, in other words, avoiding black-outs.